Examines the concepts of measurement, sources of measurement error, control, and instrumentation as they relate to variables in clinical research. Provides an opportunity to explore the procedural aspects of measurement, criterion-referenced and norm-referenced measures, as well as the reliability and validity of measurement techniques. Discusses methods and statistical procedures used in instrument design and testing, such as instrument blueprints, factor analysis, and item response theory. Emphasizes the measurement of variables to evaluate the effectiveness of clinical interventions.